Hydraulic shock absorber

ABSTRACT

A rod guide is press-fitted to the inner periphery of an outer cylinder and to the inner periphery of an inner cylinder. A rod seal is provided at the inner periphery of a cover member for covering the outer cylinder to seal between a piston rod and the cover member. The space between the rod seal and the rod guide is formed as a hydraulic fluid reservoir chamber. Further, a lip seal is integrally formed on the outer periphery of the rod seal. The lip seal is set so as to separably abut on a valve seat surface of the rod guide. One side surface of the lip seal is provided with a plurality of hydraulic fluid grooves radially extending apart from each other in the circumferential direction. With this arrangement, the valve opening pressure of the lip seal can be kept small regardless of the size of interference of the lip seal. Thus, air removability is improved.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a hydraulic shock absorbersuitable for use to damp or buffer vibrations of a vehicle, for example,an automobile.

[0002] In general, a hydraulic shock absorber has an outer cylinder, oneend of which is closed, and which has an annular cover member providedat the other end thereof. An inner cylinder is provided in the outercylinder to form an annular reservoir chamber between itself and theouter cylinder. A piston rod is inserted at one end thereof into theinner cylinder. The other end of the piston rod extends through thecover member and projects to the outside from the outer cylinder. Acylindrical rod guide is provided at the other end of the inner cylinderto guide the piston rod slidably. A rod seal is provided on the innerperiphery of the cover member in sliding contact with the outerperiphery of the piston rod to seal between the piston rod and the covermember.

[0003] With the hydraulic shock absorber according to the related artdescribed above, the one end of the outer cylinder is secured to anaxle-side member of an automobile, for example, and the other end of thepiston rod is secured to a body-side member of the automobile. Whenvibrations occur during running of the automobile or on other occasions,the piston rod extends and contracts to cause a hydraulic fluid to flowbetween a rod-side hydraulic fluid chamber and a bottom-side hydraulicfluid chamber that are formed in the inner cylinder, thereby generatingdamping force through a damping force generating mechanism includingdisk valves and so forth to damp the vibrations of the automobile.

[0004] In the related art, when the piston rod contracts or extends, thevolumetric capacity of the inner cylinder changes by an amountcorresponding to the amount by which the piston rod enters or withdrawsfrom the inner cylinder. At this time, therefore, the hydraulic fluid inthe inner cylinder is allowed to flow out into the reservoir chamber, orthe hydraulic fluid in the reservoir chamber is allowed to flow into theinner cylinder. In addition, a gas sealed in the reservoir chamber iscompressed or expanded by the action of hydraulic fluid flowing into orout of the reservoir chamber. In this way, such a volumetric change inthe inner cylinder is absorbed.

[0005] Further, in the related art, a hydraulic fluid reservoir chamberis provided between the rod seal and the rod guide. In addition, a lipseal is integrally provided on the outer periphery of the rod seal. Thelip seal is located between the reservoir chamber and the hydraulicfluid reservoir chamber to serve as a check valve. The lip sealseparably abuts on the rod guide to allow the hydraulic fluid in thehydraulic fluid reservoir chamber to flow toward the reservoir chamberand to block flow of hydraulic fluid in the reverse direction.

[0006] Accordingly, when the rod-side hydraulic fluid chamber is broughtinto a high-pressure state during extension of the piston rod, thehydraulic fluid in the hydraulic fluid chamber leaks into the hydraulicfluid reservoir chamber through the gap between the piston rod and therod guide. As a result, an excess of hydraulic fluid due to the leakageinto the hydraulic fluid reservoir chamber causes the lip seal to openand flows therethrough to return to the reservoir chamber. Thus, thepressure of hydraulic fluid in the hydraulic fluid reservoir chamber iskept from increasing excessively to prevent an excess load from actingon the lip seal.

[0007] During assembly of the hydraulic shock absorber, air enters theinner cylinder undesirably. If the hydraulic shock absorber is used inthis state, damping force characteristics obtained with the disk valvesdegrade. Therefore, in advance of shipment of products or on otheroccasions, an operator performs an air removing operation to dischargethe air in the inner cylinder into the reservoir chamber, therebypreventing degradation of the quality of the products.

[0008] More specifically, in the air removing operation, the piston rodis caused to extend and contract a plurality of times, thereby releasingthe air in the inner cylinder into the hydraulic fluid reservoir chamberthrough the gap between the piston rod and the rod guide. The releasedair opens the lip seal and is discharged into the reservoir chamberthrough the lip seal.

[0009] Incidentally, with the above-described related art, if theinterference of the lip seal abutting on the valve seat surface of therod guide is reduced to set the valve opening pressure of the lip sealat a lower level, the hydraulic fluid and air leaking into the hydraulicfluid reservoir chamber can be returned to the reservoir chambersmoothly.

[0010] However, if the valve opening pressure is reduced simply byreducing the thickness of the lip seal, some problems arise. That is,the rod seal itself or a member provided around the rod seal (e.g. therod guide) needs to be produced with some dimensional tolerances.Therefore, if the dimensional tolerances of these members are large,when the hydraulic shock absorber is assembled, the lip seal, which isintegral with the rod seal, may abut strongly on the rod guide at thewhole surface thereof, causing the interference of the lip seal tobecome larger than is needed.

[0011] In such a case, as the interference of the lip seal increases,the valve opening pressure increases. Consequently, the removability ofair from the inner cylinder degrades. In addition, variations ininterference of the lip seal due to the dimensional tolerances of therod seal and so forth make it difficult to keep the valve openingpressure of the lip seal small and uniform among products.

[0012] In the related art, further, the rod seal having the lip seal isintegrally secured to the cover member, and the cover member is securedto the other side of the outer cylinder by bending the other end of theouter cylinder against the cover member. Therefore, the interference ofthe lip seal varies also with the bending pressure applied to the covermember when secured to the other end of the outer cylinder. Accordingly,it is difficult to make the valve opening pressure of the lip sealuniform among products.

[0013] The present invention was made in view of the above-describedproblems with the related art, and an object of the present invention isto provide a hydraulic shock absorber designed so that the valve openingpressure of the lip seal can be kept small irrespective of the size ofthe interference of the lip seal, and it is possible to minimizevariations in valve opening pressure of the lip seal among products andto improve the air removability.

SUMMARY OF THE INVENTION

[0014] To solve the above-described problem, the present inventionprovides a hydraulic shock absorber including an outer cylinder, one endof which is closed, and which has an annular cover member provided atthe other end thereof. An inner cylinder is provided in the outercylinder to form an annular reservoir chamber between itself and theouter cylinder. A piston rod is inserted at one end thereof into theinner cylinder. The other end of the piston rod extends through thecover member and projects to the outside from the outer cylinder. Acylindrical rod guide is provided at the other end of the inner cylinderto guide the piston rod slidably. A rod seal is provided at the innerperiphery of the cover member in sliding contact with the outerperiphery of the piston rod to seal between the piston rod and the covermember. A hydraulic fluid reservoir chamber is formed between the rodseal and the rod guide to accommodate a hydraulic fluid leaking out ofthe inner cylinder through the rod guide. A check valve is providedbetween the reservoir chamber and the hydraulic fluid reservoir chamber.The check valve is separably seated on the rod guide to allow thehydraulic fluid in the hydraulic fluid reservoir chamber to flow towardthe reservoir chamber and to block flow of hydraulic fluid in thereverse direction. The check valve has a hydraulic fluid groove forguiding the hydraulic fluid from the hydraulic fluid reservoir chamberto an outer peripheral portion of the check valve. Preferably, the checkvalve is formed from a lip seal having an annular lip portion integrallyformed on the outer periphery of the rod seal and extending radiallyoutward. The lip portion is separably seated on the rod guide.Preferably, the lip portion of the lip seal is formed with theabove-described hydraulic fluid groove extending from the radially innerside toward the radially outer side along one side surface of the lipseal that faces the hydraulic fluid reservoir chamber.

[0015] In one embodiment of the present invention, the lip portion ofthe lip seal serving as the check valve is provided with a hydraulicfluid groove extending from the radially inner side toward the radiallyouter side along one side surface of the lip seal that faces thehydraulic fluid reservoir chamber, so that the hydraulic fluid in thehydraulic fluid reservoir chamber can be guided to the outside of thehydraulic fluid groove provided on the lip portion of the lip seal.Accordingly, even when there is an increase in the interference of thelip portion abutting on the rod guide when the lip seal is installed,the passage of the hydraulic fluid groove is ensured. Therefore, only anouter portion of the lip portion opens, and the valve opening pressureof the lip seal can be set at a low level.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a vertical sectional view of a hydraulic shock absorberaccording to an embodiment of the present invention.

[0017]FIG. 2 is a fragmentary enlarged sectional view showing a rodguide, a rod seal, a lip seal, etc. in FIG. 1.

[0018]FIG. 3 is an enlarged sectional view showing the rod seal and thelip seal in FIG. 1 as a single unit.

[0019]FIG. 4 is a bottom view of the rod seal and the lip seal as seenfrom the direction of the arrow IV-IV in FIG. 3.

[0020]FIG. 5 is a fragmentary enlarged sectional view as seen from thesame position as in FIG. 2, showing a state where the interference ofthe lip seal is reduced.

[0021]FIG. 6 is a characteristic chart showing the relationship betweenthe interference of the lip seal and the valve opening pressure thereof.

[0022]FIG. 7 is a fragmentary enlarged sectional view of a rod guide, arod seal, a lip seal, etc. in a comparative example as seen from thesame position as in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] A hydraulic shock absorber according to an embodiment of thepresent invention will be described below in detail with reference tothe accompanying drawings.

[0024] In the figures, reference numeral 1 denotes an outer cylinder,one end of which is closed. The outer cylinder 1 constitutes the body ofa hydraulic shock absorber. The lower end of the outer cylinder 1, whichis defined as one end thereof, is closed with a bottom cap 2. The upperend of the outer cylinder 1, which is defined as the other end thereof,is formed with a plurality of bent portions 1A (only two of them areshown). An annular cover plate 3 is provided at the upper end of theouter cylinder 1 as a cover member. The cover plate 3 abuts on a rodguide 11 (described later) and is secured with the bent portions 1A inthis state.

[0025] Reference numeral 4 denotes an inner cylinder coaxially providedin the outer cylinder 1. The lower end of the inner cylinder 4 is fittedto the outer periphery of a bottom valve 5 (described later). The innercylinder 4 defines an annular reservoir chamber A between itself and theouter cylinder 1. A hydraulic fluid and a gas are sealed in thereservoir chamber A.

[0026] The bottom valve 5 is provided between the bottom cap 2 and thelower end of the inner cylinder 4. The bottom valve 5 has disk valves 5Aand a check valve 5B. The bottom valve 5 operates as follows. When apiston rod 9 (described later) extends, the disk valves 5A are closed,whereas the check valve 5B opens to allow the hydraulic fluid in thereservoir chamber A to flow into a bottom-side hydraulic fluid chamber B(described later).

[0027] When the piston rod 9 contracts, the bottom valve 5 operates asfollows. The check valve 5B is closed, whereas the disk valves 5A opento allow the hydraulic fluid in the bottom-side hydraulic fluid chamberB to flow into the reservoir chamber A. At this time, the disk valves 5Agive a resistance to the flow of hydraulic fluid to generate dampingforce.

[0028] Reference numeral 6 denotes a piston slidably fitted in the innercylinder 4. The piston 6 divides the inside of the inner cylinder 4 intoa bottom-side hydraulic fluid chamber B and a rod-side hydraulic fluidchamber C. The piston 6 is provided with extension-side disk valves 7and a compression-side disk valve 8. The disk valves 7 open when thepiston rod 9 extends. The disk valve 8 opens when the piston rod 9contracts. Thus, the disk valves 7 and 8 allow the hydraulic fluid toflow between the bottom-side hydraulic fluid chamber B and the rod-sidehydraulic fluid chamber C, thereby generating damping force.

[0029] The piston rod 9 has its lower end inserted in the inner cylinder4 and secured to the inner periphery of the piston 6 with a nut 10 andso forth. The upper end of the piston rod 9 extends through a rod guide11 (described later) and the cover plate 3 and projects to the outside.

[0030] The rod guide 11 is provided at the upper end of the innercylinder 4. As shown in FIGS. 1 and 2, the rod guide 11 is formed in theshape of a triple-wall cylinder as a whole by press-forming a singlesteel plate or the like.

[0031] The rod guide 11 comprises an inner cylindrical portion 11Aloosely fitted to the outer periphery of the piston rod 9; an innerstepped expanded portion 11B connected to the lower end of the innercylindrical portion 11A through a step portion 11B1; an intermediatecylindrical portion 11C extending upward from the lower end of thestepped expanded portion 11B; an outer stepped expanded portion 11Dconnected to the upper end of the intermediate cylindrical portion 11Cthrough a step portion 11D1; and an outer cylindrical portion 11Eextending obliquely downward from the stepped expanded portion 11Dhaving an intermediate portion bent in the shape of the symbol “<” or“>”.

[0032] Regarding the rod guide 11, as shown in FIG. 2, the top surfaceof the step portion 11D1 is formed from a smoothed surface as an annularvalve seat surface 11D2. A lip seal 16 (described later) abuts on thevalve seat surface 11D2. Further, the stepped expanded portion 11D ofthe rod guide 11 is provided with a plurality of circumferentiallyspaced communicating holes 11F (only one of them is shown). Thecommunicating holes 11F provide communication between the reservoirchamber A and an annular space 18 (described later).

[0033] The rod guide 11 is installed as follows. The step portion 11D1is placed to abut on the upper end of the inner cylinder 4, and in thisstate, the intermediate cylindrical portion 11C and the outercylindrical portion 11E are press-fitted to the respective innerperipheries of the inner and outer cylinders 4 and 1. In addition, acylindrical guide seal 12 made of a resin material or the like is fittedto the inner periphery of the inner cylindrical portion 11A of the rodguide 11. The rod guide 11 has the guide seal 12 brought into slidingcontact with the outer periphery of the piston rod 9, thereby slidablyguiding the piston rod 9 in the axial direction.

[0034] Reference numeral 13 denotes a rod seal provided on the innerperiphery of the cover plate 3. The rod seal 13 is formed in acylindrical shape from an elastic material, e.g. rubber. An upper lipportion 13A is provided on the inner periphery of the upper end of therod seal 13. The inner periphery of the lower end of the rod seal 13 isprovided with a pair of lower lip portions 13B and 13C spaced apart fromeach other in the vertical direction.

[0035] Further, vertically spaced annular plate portions 13D and 13E areintegrally formed on the outer periphery of the rod seal 13. The spacebetween the annular plate portions 13D and 13E forms an annular mountingrecess 13F. With the inner periphery of the cover plate 3 fitted intothe mounting recess 13F, the rod seal 13 is secured thereto by weldingor bonding. It should be noted that the annular plate portion 13E of therod seal 13 constitutes a part of a lip seal 16 (described later). A lipportion 16A (described later) is integrally formed on the outerperiphery of the annular plate portion 13E.

[0036] The rod seal 13 has the upper lip portion 13A brought intosliding contact with the outer periphery of the piston rod 9 withinterference, and the lower lip portions 13B and 13C are brought intosliding contact with the outer periphery of the piston rod 9 withinterference by a ring-shaped coil spring 14, thereby sealing betweenthe piston rod 9 and the cover plate 3 in a fluid-tight and gas-tightmanner. Reference numeral 15 denotes a hydraulic fluid reservoir chamberprovided between the rod guide 11 and the rod seal 13. The hydraulicfluid reservoir chamber 15 is formed as an annular space between thepiston rod 9, the rod guide 11, the rod seal 13 and the lip seal 16.When the hydraulic fluid in the rod-side hydraulic fluid chamber C orair mixed in the hydraulic fluid leaks out through a slight gap betweenthe piston rod 9 and the guide seal 12, the hydraulic fluid reservoirchamber 15 accommodates the leaked hydraulic fluid or air.

[0037] Reference numeral 16 denotes a lip seal provided on the outerperiphery of the rod seal 13 as a check valve. The lip seal 16 is formedtogether with the rod seal 13 by integral molding. The lip seal 16 ispreferably formed from an elastic material, e.g. rubber. The lip seal 16comprises an annular plate portion 13E integrally formed on the outerperiphery of the rod seal 13 and an annular lip portion 16A. Theproximal end of the annular lip portion 16A is integrally formed on theouter periphery of the annular plate portion 13E. The distal end of thelip portion 16A extends obliquely downward at the radially outer sidethereof. The lip portion 16A of the lip seal 16 has one side surface 16Bfacing the hydraulic fluid reservoir chamber 15 and the other sidesurface 16C facing an annular space 18 (described later). The one sidesurface 16B is provided with hydraulic fluid grooves 17 (describedlater).

[0038] Further, the lip portion 16A of the lip seal 16 has a distal endportion located at the outer peripheral end thereof. The distal endportion of the lip portion 16A extends downward as viewed in the figuresfrom the outer peripheral end. In this embodiment, the distal endportion of the lip portion 16A forms an annular valve portion 16D thatabuts on the valve seat surface 11D2 of the rod guide 11 withinterference. The valve portion 16D is adapted to separate from or reston the valve seat surface 11D2 in accordance with the pressure ofhydraulic fluid or air in the hydraulic fluid reservoir chamber 15 thatacts between the valve seat surface 11D2 of the rod guide 11 and the oneside surface 16B.

[0039] The lip seal 16 allows the hydraulic fluid in the hydraulic fluidreservoir chamber 15 to flow into the reservoir chamber A through theannular space 18 and the communicating holes 11F of the rod guide 11 andblocks flow of hydraulic fluid in the reverse direction.

[0040] Reference numeral 17 denotes hydraulic fluid grooves provided onthe lip portion 16A of the lip seal 16 apart from each other in thecircumferential direction. The number of hydraulic fluid grooves ispreferably six by way of example. The hydraulic fluid grooves 17 areformed by cutting the one side surface 16B of the lip seal 16 to provideapproximately rectangular notches extending from the radially inner sidetoward the radially outer side along the one side surface 16B.

[0041] Further, the hydraulic fluid grooves 17 are arranged on the oneside surface 16B of the lip seal 16 at approximately equal intervals inthe circumferential direction to extend radially. Furthermore, thehydraulic fluid grooves 17 are located radially inside the valve portion16D of the lip portion 16A of the lip seal 16.

[0042] As shown in FIG. 2, the hydraulic fluid grooves 17 are formed bylocally reducing the wall thickness of the lip portion 16A to guide thehydraulic fluid to the valve portion 16D through passages formed betweenthe hydraulic fluid grooves 17 and the valve seat surface 11D2 of therod guide 11. Thus, only the valve portion 16D opens, and it isconsequently possible to set the valve opening pressure of the lip seal16 as a check valve at a low level.

[0043] Reference numeral 18 denotes an annular space formed between thecover plate 3, the rod guide 11 and the lip seal 16. A seal ring 19 issecured to the outer periphery of the cover plate 3. The seal ring 19prevents the hydraulic fluid and gas in the reservoir chamber A fromleaking to the outside through the joint between the outer cylinder 1and the cover plate 3.

[0044] The hydraulic shock absorber according to this embodiment has theabove-described structure. The upper end of the piston rod 9 is securedto a body-side member of an automobile through a mount rubber and soforth (not shown). The lower end of the outer cylinder 1 is secured toan axle-side member of the automobile through a mounting eye 20 and soforth. When vibrations occur during running of the automobile or onother occasions, the hydraulic shock absorber allows the piston rod 9 toextend and contract, and while doing so, generates damping force throughthe disk valves 7 and 8 to damp the vibrations.

[0045] More specifically, during the extension stroke of the piston rod9, the inside of the rod-side hydraulic fluid chamber C is placed underhigh pressure. Therefore, the hydraulic fluid in the hydraulic fluidchamber C flows out into the bottom-side hydraulic fluid chamber Bthrough the disk valves 7, causing damping force to be generated. Atthis time, an amount of hydraulic fluid corresponding to the volumetriccapacity of the portion of the piston rod 9 protruded from the innercylinder 4 flows out of the reservoir chamber A and enters thebottom-side hydraulic fluid chamber B through the check valve 5Bconstituting the bottom valve 5. In addition, the pressure of gas in thereservoir chamber A is reduced, thereby absorbing the volumetric changecorresponding to the volumetric capacity of the portion of the pistonrod 9 by which it has withdrawn from the inner cylinder 4.

[0046] At this time, because the pressure in the rod-side hydraulicfluid chamber C is increased, the hydraulic fluid in the hydraulic fluidchamber C may leak into the hydraulic fluid reservoir chamber 15 througha slight gap between the piston rod 9 and the guide seal 12, forexample. In such a case, an excess of hydraulic fluid resulting from theleakage of hydraulic fluid into the hydraulic fluid reservoir chamber 15causes the lip seal 16 to separate from the valve seat surface 11D2 ofthe rod guide 11 and flows into the annular space 18 to return to thereservoir chamber A through the communicating holes 11F. During thecompression stroke of the piston rod 9, the bottom-side hydraulic fluidchamber B is placed under high pressure. Therefore, the hydraulic fluidin the hydraulic fluid chamber B flows out into the rod-side hydraulicfluid chamber C through the disk valve 8, causing damping force to begenerated. At this time, an amount of hydraulic fluid corresponding tothe volumetric capacity of the portion of the piston rod 9 by which ithas entered the inner cylinder 4 flows out of the bottom-side hydraulicfluid chamber B and enters the reservoir chamber A through the diskvalves 5A of the bottom valve 5 to pressurize the gas in the reservoirchamber A, causing the lip seal 16 to be pressed against the valve seatsurface 11D2 of the rod guide 11. In addition, the flow of hydraulicfluid into the reservoir chamber A absorbs the volumetric changecorresponding to the volumetric capacity of the portion of the pistonrod 9 by which it has entered the inner cylinder 4.

[0047] Meanwhile, when air entering the inner cylinder 4 during theassembly of the hydraulic shock absorber is to be discharged into thereservoir chamber A, the piston rod 9 is caused to extend and contract aplurality of times, thereby allowing the air in the inner cylinder 4 tobe released into the hydraulic fluid reservoir chamber 15 through thegap between the piston rod 9 and the guide seal 12. The air releasedinto the hydraulic fluid reservoir chamber 15 causes the lip seal 16 toopen. Thus, the air can be discharged into the reservoir chamber A.

[0048] Incidentally, if the interference of the lip seal 16 abutting onthe valve seat surface 11D2 of the rod guide 11 is reduced to set thevalve opening pressure of the lip seal 16 at a lower level as shown inFIG. 5, the air released into the hydraulic fluid reservoir chamber 15as stated above can be smoothly returned to the reservoir chamber Athrough the lip seal 16, and hence the removability of air from theinner cylinder 4 can be improved.

[0049] However, the rod seal 13 itself, including the lip seal 16, or amember provided around the rod seal 13 (e.g. the rod guide 11) needs tobe produced with some dimensional tolerances. Therefore, if thedimensional tolerances of these members are large, when the hydraulicshock absorber is assembled, the lip seal 16, which is integral with therod seal 13, may abut strongly on the rod guide 11 not only at the lowerend of the valve portion 16D but also at a part of the one side surface16B, as shown in FIG. 2, causing the interference of the lip seal 16 tobecome unfavorably large.

[0050] Therefore, the lip seal 16 used in this embodiment is arranged sothat the one side surface 16B of the lip portion 16A, which faces thehydraulic fluid reservoir chamber 15, is provided with the hydraulicfluid grooves 17 extending from the radially inner side toward theradially outer side.

[0051] Thus, even when the interference of the lip portion 16A abuttingon the valve seat surface 11D2 of the rod guide 11 increases during theinstallation of the lip seal 16, it is possible to guide the hydraulicfluid from the hydraulic fluid reservoir chamber 15 to the valve portion16D through the hydraulic fluid grooves 17 and to open only the valveportion 16D of the lip portion 16A. As a result, the valve openingpressure of the lip seal 16 can be set at a low level.

[0052] Thus, in this embodiment, the valve opening pressure of the lipseal 16 can be kept low irrespective of the size of the interference ofthe lip portion 16A as shown by the solid-line characteristic curve F inFIG. 6. Accordingly, it is possible to improve the removability of airfrom the inner cylinder 4 through the lip seal 16 and hence possible tomaintain high damping force characteristics of the disk valves 7 and 8.

[0053] Moreover, because the valve opening pressure of the lip seal 16can be lowered as stated above, the pressure of hydraulic fluid in thehydraulic fluid reservoir chamber 15 can be kept from increasingexcessively when the piston rod 9 extends or contracts. Consequently, itis possible to prevent an excess load from acting on the lip seal 16 andalso prevent the hydraulic fluid in the hydraulic fluid reservoirchamber 15 from leaking to the outside.

[0054] In contrast, if there are no hydraulic fluid grooves 17 in thelip portion 16A′ of the lip seal 16′ as in a comparative example shownin FIG. 7 or if the stiffness or rigidity of the lip seal 16′ is merelyreduced (i.e. the thickness thereof is reduced), the valve openingpressure of the lip seal 16′ rises as the interference of the lip seal16′ increases, as shown by the dotted-line characteristic curve f inFIG. 6. Consequently, the removability of air through the lip seal 16′degrades.

[0055] Accordingly, with this embodiment the valve opening pressure ofthe lip seal 16 can be set at an approximately constant small valueregardless of whether the bending pressure applied through the bentportions 1A is increased or reduced when the cover plate 3 integrallyprovided with the rod seal 13 is secured to the outer cylinder 1 throughthe bent portions 1A. Thus, it is possible to reduce variations in valveopening pressure of the lip seal 16 among products and hence possible toimprove the hydraulic shock absorber in performance and reliability.

[0056] In addition, the distal end of the lip portion 16A of the lipseal 16 is arranged to serve as the valve portion 16D that abuts on thevalve seat surface 11D2 of the rod guide 11, and the hydraulic fluidgrooves 17 are provided radially inside the valve portion 16D.Therefore, a sufficient wall thickness can be ensured for the valveportion 16D, and the valve portion 16D can be allowed to abut on thevalve seat surface 11D2 of the rod guide 11 stably with interference.Thus, the sealing function of the lip seal 16 serving as a check valvecan be maintained at a high level.

[0057] Further, a plurality of circumferentially spaced hydraulic fluidgrooves 17 are provided along the one side surface 16B of the lip seal16. Therefore, when the lip seal 16 is to be opened, the valve portion16D can be separated from the valve seat surface 11D2 of the rod guide11 at each of the hydraulic fluid grooves 17. Thus, the hydraulic fluidgrooves 17 allow the hydraulic fluid and air in the hydraulic fluidreservoir chamber 15 to be discharged into the reservoir chamber A evenmore smoothly. Although in the foregoing embodiment six hydraulic fluidgrooves 17 are provided on the lip seal 16 by way of example, it shouldbe noted that more or less than six hydraulic fluid grooves, forexample, may be provided according to the hardness of the material, e.g.rubber, on the assumption that the pressure in the hydraulic fluidreservoir chamber 15 is held approximately at a predetermined level(i.e. such a pressure that the hydraulic fluid will not leak to theoutside). It is also possible to provide hydraulic fluid groovesextending over the whole circumference.

[0058] Further, although in the foregoing embodiment the presentinvention has been described with regard to a hydraulic shock absorberfor use in an automobile by way of example, the present invention is notnecessarily limited thereto but may also be applied, for example, tohydraulic shock absorbers used in various machines, architecturalstructures, etc. that constitute vibration sources.

[0059] As has been detailed above, in the foregoing embodiment areservoir chamber is formed between an outer cylinder and an innercylinder, and a hydraulic fluid reservoir chamber is formed between arod seal provided at the other end of the outer cylinder and a rod guideprovided at the other end of the inner cylinder. A check valve isprovided between the reservoir chamber and the hydraulic fluid reservoirchamber to allow only the flow of hydraulic fluid from the hydraulicfluid reservoir chamber to the reservoir chamber. The check valve isconstructed as a lip seal having an annular lip portion integrallyformed on the outer periphery of the rod seal and separably seated onthe rod guide. The lip portion of the lip seal is formed with hydraulicfluid grooves extending from the radially inner side toward the radiallyouter side along one side surface of the lip seal that faces thehydraulic fluid reservoir chamber. Therefore, even when the interferenceof the lip portion separably seated on the rod guide is increased, thehydraulic fluid in the hydraulic fluid reservoir chamber can be guidedto the outer peripheral portion of the lip portion through the hydraulicfluid grooves so as to open the outer peripheral portion of the lipportion.

[0060] Thus, the valve opening pressure of the lip seal can be kept lowregardless of the size of the interference of the lip portion.Accordingly, it is possible to improve the removability of air from theinner cylinder through the lip seal and hence possible to maintain highdamping force characteristics of the hydraulic shock absorber. Further,because the valve opening pressure of the lip seal can be kept low, thepressure of hydraulic fluid in the hydraulic fluid reservoir chamber canbe kept from increasing excessively when the piston rod extends orcontracts. Therefore, it is possible to prevent an excess load fromacting on the lip seal and also prevent the hydraulic fluid in thehydraulic fluid reservoir chamber from leaking to the outside.

[0061] The entire disclosure of Japanese Patent Application No.2000-130145 filed on Apr. 28, 2000 including specification, claims,drawings and summary is incorporated herein by reference in itsentirety.

What is claimed is:
 1. A hydraulic shock absorber comprising: an outercylinder having one end and an opposite end, said one end being closed;an annular cover member provided at the opposite end of said outercylinder; an inner cylinder having one end associated with the one endof said outer cylinder, said inner cylinder further having an oppositeend associated with the opposite end of said outer cylinder, and saidinner cylinder being provided in said outer cylinder to form an annularreservoir chamber between itself and said outer cylinder; a piston rodhaving one end and an opposite end, said one end being inserted intosaid inner cylinder, said the opposite end extending through said covermember and projecting to an outside from said outer cylinder; acylindrical rod guide provided at the opposite end of said innercylinder to guide said piston rod slidably; a rod seal provided at aninner periphery of said cover member in sliding contact with an outerperiphery of said piston rod to seal between said piston rod and saidcover member; a hydraulic fluid reservoir chamber formed between saidrod seal and said rod guide to accommodate a hydraulic fluid leaking outof said inner cylinder through said rod guide; a communicating holeprovided in said rod guide to provide communication between saidhydraulic fluid reservoir chamber and said reservoir chamber; and acheck valve provided between said communicating hole and said hydraulicfluid reservoir chamber, said check valve separably resting on a valveseat surface of said rod guide to allow the hydraulic fluid in saidhydraulic fluid reservoir chamber to flow toward said reservoir chamberthrough said communicating hole and to block flow of hydraulic fluidfrom said reservoir chamber toward said hydraulic fluid reservoirchamber; wherein said check valve has a hydraulic fluid groove forguiding the hydraulic fluid from said hydraulic fluid reservoir chamberto an outer peripheral portion of said check valve.
 2. A hydraulic shockabsorber according to claim 1, wherein said check valve has one sidesurface facing said hydraulic fluid reservoir chamber, said hydraulicfluid groove being formed on said one side surface.
 3. A hydraulic shockabsorber according to claim 2, wherein said hydraulic fluid grooveextends from a radially inner side of said check valve toward a radiallyouter side thereof.
 4. A hydraulic shock absorber according to claim 3,further comprising a plurality of hydraulic fluid grooves provided apartfrom each other in a circumferential direction.
 5. A hydraulic shockabsorber according to claim 4, wherein said plurality of hydraulic fluidgrooves are provided at approximately equal intervals in thecircumferential direction.
 6. A hydraulic shock absorber according toclaim 2, wherein said hydraulic fluid groove is in a shape of anapproximately rectangular recess.
 7. A hydraulic shock absorberaccording to claim 1, wherein said check valve has a lip seal integrallyformed on an outer periphery of said rod seal.
 8. A hydraulic shockabsorber according to claim 7, wherein said lip seal has a surfacefacing said hydraulic fluid reservoir chamber, said hydraulic fluidgroove being formed on said surface.
 9. A hydraulic shock absorberaccording to claim 8, wherein said lip seal has an annular plate portionintegrally formed on the outer periphery of said rod seal and an annularlip portion extending radially outward from said annular plate portion,said annular lip portion having a proximal end and a distal end, theproximal end of said annular lip portion being integrally formed on anouter periphery of said annular plate portion.
 10. A hydraulic shockabsorber according to claim 9, wherein the distal end of said annularlip portion extends obliquely downward at a radially outer side thereof.11. A hydraulic shock absorber according to claim 10, wherein said lipportion has one side surface facing said hydraulic fluid reservoirchamber and an opposite side surface facing said cover member, saidhydraulic fluid groove being provided on said one side surface.
 12. Ahydraulic shock absorber according to claim 11, wherein said hydraulicfluid groove has a shape of a recess extending from a radially innerside of said lip portion toward a radially outer side thereof, and as aresult of providing said hydraulic fluid groove having a recess shape,said lip portion is formed with an annular valve portion at the distalend located at an outer periphery thereof, said annular valve portionseparably resting on the valve seat surface of said rod guide.
 13. Ahydraulic shock absorber according to claim 12, wherein said annularvalve portion is capable of abutting on the valve seat surface of saidrod guide with interference.
 14. A hydraulic shock absorber according toclaim 13, further comprising a plurality of hydraulic fluid groovesprovided apart from each other in a circumferential direction.
 15. Ahydraulic shock absorber according to claim 14, wherein said pluralityof hydraulic fluid grooves are provided at approximately equal intervalsin the circumferential direction.
 16. A hydraulic shock absorberaccording to claim 15, wherein each of said hydraulic fluid grooves isin a shape of an approximately rectangular recess.
 17. A hydraulic shockabsorber according to claim 1, wherein an annular space is formedbetween said cover member, said rod guide and said check valve, saidannular space communicating with said reservoir chamber through thecommunicating hole of said rod guide.
 18. A hydraulic shock absorberaccording to claim 17, wherein said check valve is movable toward saidannular space according to a differential pressure between saidhydraulic fluid reservoir chamber and said reservoir chamber.